1. Field of the Invention
The present invention relates to a position controller for an optical element.
2. Description of the Related Art
A type of image shake correcting mechanism (shake reduction mechanism/image stabilizing mechanism) which moves an optical element such as a lens element or an image sensor (image pickup device) in a plane orthogonal to an optical axis of an optical system (this optical element is hereinafter referred to as an image-shake-correcting optical element) to reduce image shake in an optical device such as a camera has been often used in recent years. The assignee of the present invention has proposed a structure for this type of image shake correcting mechanism wherein the moving range of the image-shake-correcting optical element is set to be greater than the effective moving range thereof for use in image shake correction (image shake reduction) to move the image-shake-correcting optical element to a position removed from an optical path, when an optical device that incorporates the image shake correcting mechanism moves from an operating state to a non-operating state. This structure is disclosed in Japanese Unexamined Patent Publication 2006-154674 (U.S. Pat. No. 7,630,618 B2).
Specifically, according to this proposed structure, a movable frame, which supports an image sensor (image-shake-correcting optical element) and is movable in a direction orthogonal to an optical axis of an optical system, is moved by a mechanism for use in image shake correction within an anti-shake driving range (in which the image sensor is positioned on the optical axis) in a ready-to-photograph state or moved by a different mechanism for displacing the image sensor to a position where the image sensor is removed from a position on the optical axis when a lens barrel (retractable lens barrel) moves from a ready-to-photograph state to an accommodated state (fully-retracted state). The image sensor displacing (removing) mechanism is provided with a swing member which is driven to swing about an axis parallel to the optical axis, and this swing member presses the movable frame toward a removed position that is eccentric from the optical axis when the lens barrel moves from a ready-to-photograph state to the accommodated state. On the other hand, when the lens barrel moves from the accommodates state to a ready-to-photograph state, the swing member stops pressing the movable frame, so that the movable frame returns into the anti-shake driving range, in which the image sensor is positioned on the optical axis. The returning operation of the movable frame into the anti-shake driving range is performed by a biaser, and the image sensor displacing mechanism is provided with a stopper which prevents the movable frame from moving in the biasing direction of the biaser. The stopper is a part of the image shake correcting mechanism, and the position of the movable frame can be changed within the anti-shake driving range by changing the position of the stopper by driving a motor for image shake correction. With the above described structure of the image sensor displacing mechanism, the image-shake-correcting optical element (image sensor) which is removed to a position that is eccentric from an optical axis and another optical element (a lens group or the like) which remains on the optical axis can be positioned to lie in a plane orthogonal to the optical axis to thereby make it possible to achieve a reduction in length of the optical system in the optical axis direction when the optical device is in a non-operating state. In addition, in regard to the support structure for the image-shake-correcting optical element, a simplification of the structure can be achieved by allowing the movable frame to move to the removed position by an extension of a guide mechanism that is used for image shake correction (by making the guide mechanism sharable between the image shake correction system and the image sensor displacing system).
In the above-mentioned patent publication, when the movable frame is in the anti-shake driving range, the image shake correcting operation is performed by changing the position of the stopper, which is in contact mechanically with the movable frame, by driving a motor. Alternatively, an image shake correcting mechanism like that disclosed in Japanese Unexamined Patent Publication 2006-146125 which uses an electromagnetic actuator equipped with coils and magnets is also known in the art.
The image shake correcting mechanism disclosed in the above-mentioned Japanese Unexamined Patent Publication 2006-154674 (U.S. Pat. No. 7,630,618 B2) has a mechanical positioning structure in which the movable frame abuts against the stopper by the biasing force of the biaser, thus being capable of holding the image-shake-correcting optical element in the anti-shake driving range even when the passage of current through the motor for image shake correction is cut off or if an impact which may cause the movable frame to move to the removed position thereof that is eccentric from an optical axis acts on the image shake correcting mechanism. In contrast, an image shake correcting mechanism using an electromagnetic actuator such as that disclosed in the above-mentioned Japanese Unexamined Patent Publication 2006-146125 has a non-contact holding structure which does not include any member which comes in contact with the movable frame to mechanically control the position thereof, and accordingly, there is a possibility of the image-shake-correcting optical element deviating from the anti-shake driving range and becoming incapable of moving back into the anti-shake driving range due to a de-energization of the electromagnetic actuator or due to an external impact if the moving range of the movable frame is extended to the removed position, which is eccentric from an optical axis, in a manner such as disclosed in the above-mentioned Japanese Unexamined Patent Publication 2006-154674 (U.S. Pat. No. 7,630,618 B2).